Electronic devices use power to operate. Switched mode power converters are commonly used due to their high efficiency, small size and low weight to power many of today's electronics. Conventional wall sockets provide a high voltage alternating current. In a switching power converter, a high voltage alternating current (ac) input is converted to provide a well regulated direct current (dc) output through an energy transfer element to a load. In operation, a switch is utilized to provide the desired output by varying the duty cycle (typically the ratio of the ON time of the switch to the total switching period), varying the switching frequency, or varying the number of pulses per unit time of the switch in a power converter.
The power converter also includes a controller. The controller may control the switch in response to a sensed parameter of the power converter. Properties, such as efficiency, size, weight and cost are usually taken into account when designing a power converter and controller. Power converters and controllers may also be designed to meet standards set by regulatory agencies. For example, wall sockets provide an ac voltage which has a waveform conforming to standards of magnitude, frequency, and harmonic content. However, the characteristics of the current waveform drawn from the wall socket are determined by the power converter which receives the ac voltage. Regulatory agencies may set limits on magnitudes of specific frequency components of an ac current or limit the rms value of the current in accordance with the amount of power the wall socket provides. Power factor and total harmonic distortion (THD) may be used as measurements to determine if a power converter is meeting the standards set by regulatory agencies.